Radio apparatus



W. P. PLACE IO APPARATUS Filed 1952 W o gm 7 6 5 [0 i I i F LNVENTORWillard A p e H18 ATTORNEY Patented July 11, 1933 UNITED STATES PATENTOFFICE .WILLARD P. PLACE, WILKINSBURG, PENNSYLVANIA, vASSIGNOR TO THEUNION SWITCH 8c SIGNAL OOIVIl-ANY, OF SWISSVALE. PENNSYLVANIA, ACORPORATION OF PENNSYLVANIA RADIO APPARATUS Application filed August 25,1332. Serial No. 630,435.

My invent-ion relates to an electrical circuit adapted for optional useeither as a radio receiver employing a metal oxide rectifier as adetector or as an amplifying and reproducing unit for attachment tophonogra'phs or the like. The new circuit requires but few elements inaddition to those employed during radio reception and may be. readilyconverted from a radio receiver to an amplifier 10 and reproducer forphotographs by manipulation of simple throw-over switches.

lVhen it is desired to use elements of the conventional type of radioreceiver for amplifying and reproducing a phonograph rec- 0rd, themagnetic pick-up of the phonograph is connected'with the detector tubeof the receiving circuit so as to cause that tube to operate as an audiofrequency amplifier; the amplificationeifectcd thereby together withthat effected by the usual additional stage of amplification precedingthe power tube, providing sufiicient amplification for the relativelylow voltage delivered by the magnetic pick-up. This method is predicatedupon the inclusion of a tube type of detector and of a stage of audiofrequency amplification in the radio receiver. Recently there has beendeveloped a new type of radio receiver which utilizes a full wave metaloxide rectifier as a detector and requires no audio frequency stage ofamplification; the rectifier preferably feeding directly into a powertube connected to the loud speaker. Thus the usual method abovedescribed for converting a radio receiver into an amplifier andreproducer is not applicable to this new type of receiver because therewould be insufficient amplification if the magnetic pick-up wereconnected directly to the input terminals of the power tube. A step-uptransformer between the pick-up and power tube, while increasing thevolume. would result in a considerable sacrifice in the quality ofreproduction and would increase the load on the picsup with consequentundue record wear..

The circuit of the present invention makes possible the conversion of aradio receiver utilizing a metal-oxide rectifier into an amplifying andreproducing unit for phonographs while insuring sufficient volume ofreproduction without loss in quality or undue recordwear and without theprovision of an additional stage of amplification. In the new circuitthe additional audio frequency amplification required for phono-vgraphic reproduction is obtained by causing a tube which operates as aradio frequency amplifier during radio reception to be operated as anaudio frequency amplifier When the circuit is connected to the magneticpick up the circuit connections being such that the rectifier servessimply as a negligibly small capacity path to ground during phonographicreproduction.

For a better understanding of the invention reference may be had to theaccompanying drawings of which:

Fig. 1 represents diagrammatically a radio receiving circuit which, whenconverted into an amplifying and reproducing unit for )honographsincludes a single stage of audio amplification between the phonographand power tube; and v Fig. 2 represents diagrammatically a circuitsubstantially similar to that of Fig. 1

but including also a step-up transformer operable when the circuit isused for reproduction to increase the volume of sound delivered by theloud speaker.

The circuit of Fig. 1 includesthe amplifierl, having its control gridand cathode connected across the input terminals 2 of the circuit, thefull wave metal oxide rectifier 3 and the power tube 4, the outputcircuit of which is coupled to the loud speaker 5 by means of atransformer 6. The anode of tube 1 is connected through a capacity 7with one input terminal of the rectifier; the other input terminal ofthe rectifier being connected to the cathode of tube 1 throughcapacities 8 and 9. A radio frequency choke coil 10, offering negligibleimpedance to currents of audio frequency has one end connected to theplate of tube 1 and its other end connected intermediate capacities 8and 9. A variable capacity 11, connected across the inputterminals ofrectifier 3, serves, together with coil 10, to compensate for theinherent capacity of the rectifier.

A resistor 12 grounded at one end, is conare connected in series acrossresistance 12v to provide a branch for the alternating component of therectifier output current corresponding to the modulation current. Theadjustable tap along potentiometer 14 is connected to the control gridof power tube -31. A battery 15, having its positive terminal connectedthrough an iron cored inductor 16 to the end of inductor 10 connected toca pacities 8 and 9 supplies plate voltage to tube 1 and batteries 17and 18 supply positive potentials to the screen. grid and anoderespectively of tube 4. Inductor 16 has a negligible direct currentresistance and a practically infinite alternating current reactance.Batteries 15, 17 and 18 are each grounded at their negative terminalsand the c: thodes of each of tubes 1 and 4 are connectcd to groundthrough grid biasing resistors 19 and 20 respectively. Capacities 21 and22 for by-passing high frequency currents bridge resistors 19 and 20,respectivel lVhen a high frequency voltage corresponding to a modulatedcarrier wave is impressed across terminals 2, it is amplified by tube1', operating as a radio frequency amplifier, and delivered to rectifier3 through the medium of inductance 10 and capacities T. 11 and 8. Thealternating component of pulsating direct current output of therectifier is conducted by capacity 13 to potentiometer 1 1. Acontrollable portion of the voltage across potentiometer 14 is appliedto the control grid of the tube 1 for transmission to the loudspeaker 5.V

As capacity 9 by-passes inductance 16 by providing an alternative pathto ground for the radio frequency currents, inductance 16 has no effectupon the operation of the circuit when used as a radio receiver.

In order to make the above receiving circuit readily convertible into anamplifier and reproduc r for phcnographs it is only necessary to breakthe circuit at two points, namely between the cathode of tube l andcapacity 9 of rectifier 3 and the grounded end of resistor 12 and toconnect the ungrounded end of potentiometer 1 1; with the side ofcapacity 9 formerly connected to the cathode of tube 1. Switches 23 and2st and a conductor 25 areprovided for effecting these changes. Switch23, which is a single pole double throw switch, has its movablecontact'connected to one side of capacity 9. one of its fixed contactsconnected to the cathode of tube land the other of its fixed contacts"to the ungrounded end of potentiometer resistance 14. Switch 24 isinserted in the connection between one output terminal of the rectifierand the grounded end of resistor 12.

\Vhen switch 21 is opened and switch 23 thrown to connect conductor 25with capacity 9, the circuit will operate to amplify audio frequencyvoltage applied to terminal 2. Thus, with terminal 2 connected to themagnetic pick-up of a phonograph, tube 1 eperates as an audio frequencyamplifier and the alternating voltage appearing at the anode thereofapplied directly to potentiomcter rcsistence 1 1- by means of inductor16 and capacity 9.

Power tube a then further amplifies a c011- troll able portion of thevoltage across potentiometer 1% and delivers it to the loud-speakerthrough transformer 6. As inductor 10 offers practically negligiblereactance to audio frequency currents, capacity 9 may be considered asif directly connected with the anode of tube 1. I made up of capacities7, 8 and 11 and of rectifier 3 has no effect upon the remainder of thecircuit except to provide a negligibly small capacity pathto groundthrough resistor 12.

The circuit of Fig. 2 differs from that of Fig. 1 only in that anauto-transformer26 is connected in lead 25; one end of the transformerbeing connected to the ungrounded end of resistor 14, the other end ofthe transformer being grounded and the'mid point thereof being connected'to the fixed contact of switch 23. The secondary inductance oftransformer 26 is high enough sothat no appreciable loss of audiofrequency voltage applied to potentiometer l lwill occur when thecircuit is used as a radio receiver. 'VVhen used as an audio frequencyamplifier and reproducer for phonograph transformer 26 serves to step-upthe voltage applied to the power tubeand hence to increase the availablerange of audio amplification.

'It will be apparent from the above description that a radio receiverutilizing a metal oxide type of rectifier and having no stage of audiofrequency amplification preceding the power output tube, in accordancewith the invention may be readily converted into an amplifier andreproducer for phonographs by the addition of few elements, namely apair of switches and an inductor having high alternating currentimpedance and negligible resistance and, if desired, an auto transformerfor increasing the range of amplification; the additional elements beingso included in the circuit as not to intcrfere with the proper operationof the circuit when used as a radio receiver and as to cause a tubenormally'operating asa radio frequency amplifier to perform as an audiofrequency amplifier when the circuit is used for phonographicreproduction.

The new radio receiving circuit disclosed The part of the circuit hereinforms the subject matter of other applications filed by me asfollo'wsSerial No. 540348, filed May 27, 1931, Serial No. 566 107, filedOct. 2, 1931, Serial No. 569%80, filed Oct. 17, 1931, Serial No. 633273,filed Sept. 15, 1932; the present application being directed to thecombination with such receiver of elements which make possible its useeither as a receiver or as an amplifying and reproducing unit.

Although I have herein shown and described only two forms of apparatusembodying my invention, it is understood that various changes andmodifications may be made therein within the scope of the appendedclaims without departing from the spirit and scope of my invention. 7

Having thus described my invention, what I claim is:

1. A radio receiver including an amplifier, a full wave metal oxiderectifier coupled to the output circuit of said amplifier and a powertube coupled to the output circuit of said rectifier, and manuallyoperable means in the output circuits of said amplifier and of saidrectifier adapted when operated to convert said circuit into anamplifying and reproducing unit for phonographs with said amplifierserving as an audio frequency amplifier and said rectifier effectivelyby-passed.

2. A radio receiver according to claim 1 wherein the plate circuit ofsaid amplifier includes an inductor of negligible direct currentresistance and high alternating current impedance and the output circuitof said amplifier includes a capacity normally providing a by-pass foralternating currents about said inductor, said manually operable-meansin the amplifier output circuit serving when operated to connect theplate of said amplifier to the input of said power tube through saidcapacity.

3. An electric circuit adapted for use as a radio receiver andconvertible into an amplifier and reproducer for phonographs or the likecomprising in combination an amplifying tube, a metal oxide rectifiercoupled to r the output circuit of said tube, a power tube coupled tothe output circuit of said rectifier and a reproducer coupled to theoutput circuit of said power tube, an inductor in the plate circuit ofsaid amplifying tube and a capacity having one side connected to the lowpotential side of said inductor and its other side adapted forconnection to the oathode of said amplifying tube to bypass alternatingcurrents about said inductor during operation of said amplifying tube asa radio frequency amplifier and of said circuit as a radio receiver orfor connection to the input circuit of said power tube to impress altersaid circuits as an amplifier and reproducer.

a. An electric circuit according to claim 3 including an autotransformer connected to the input circuit of said power tube, saidcapacity when disconnected from the cathode of said amplifier beingconnected through said transformer with the input circuit of said powertube whereby the alternating voltages amplified by said amplifier arestepped up by said transformer and impressed upon said power tube whenthe circuit is used as an amplifying and reproducing unit.

5. An electric circuit comprising in combination an amplifier, a metaloxide rectifier v having its input terminals coupled to the outputcircuit of said amplifier, the output circuit of said rectifier beingdivided into two branches, one for the dissipation of the steady directcurrent component and one for the alternating current component of therectifier output corresponding respectively to the carrier current andto the modulation current when a modulated carrier wave is impressedupon said amplifier, a switch in the output circuit of said rectifieradapted when open to disconnect one output terminal of said rectifierfrom said branches, a power tube, means for impressing upon said powertube a controllable portion of the voltage across said alternatingcurrent branch and a reproducer coupled to the output circuit of saidpower tube, a source of. plate potential for said amplifier and twoinductorsconnected in series between said source and the plate of saidamplifier, a capacity having one side connected to the plate circuit ofsaid amplifier intermediate said conductors and manually operable meansfor connecting the other side of said capacity either to the cathode ofsaid amplifier to provide a bypass for alternating current about one ofsaid inductors or to the said alternating current branch of therectifier ouput circuit, the rectifier being connected across the otherof said inductors whereby when said switch in the rectifier outputcircuit is closed and said capacity is connected to the cathode of saidamplifier the circuit operates as a radio receiver and when said switchis open and said capacity is connected to said alternating. currentbranch said circuit operates as an audio frequency amplifier andreproducer.

In testimony whereof I atfiX my signature.

WILLARD P. PLACE.

